Fundamental to all of Mrs Sargeant’s grounds of challenge was the central submission that it was unlawful for the First Minister – the subject of the investigation – to set the terms of the OP.

She argued in particular that a public statement by the First Minister on 10 November 2017 was misleading. This stated in terms that the work necessary for the investigation to take place would be done "separately from this office" (i.e. the First Minister's Office).

However, it transpired that the First Minister had already given the Permanent Secretary, Shan Morgan, a 'remit' in private as to how the investigation should be established and the basic procedure to be followed.

In the Divisional Court Lord Justice Haddon-Cave and Mr Justice Swift agreed that the statement had given Mrs Sargeant “a legitimate expectation” that the inquiry and its procedures would be set up and decided by the Permanent Secretary, independently of the First Minister.

The judges said: “It would – in layman's terms – be unfair for the First Minister both to retain the political capital of the announcement that the work necessary to establish the Investigation would be undertaken independently from his office, and to retain the power to decide what the arrangements for the Investigation should be.

“In our view, because of the 10th November 2017 Press Statement, it was also unlawful for him to do this. On this ground alone, we allow the claimant's application for judicial review.”

In reaching their conclusions, the judges rejected the First Minister’s office contention that the statement was merely an indication of present, rather than future, intention, and that it should have been obvious that Ms Morgan was working to a careful remit given to her by the First Minister.

“The Press Statement was designed to reassure the [Sargeant] family and the public at large, in the light of the public concern following Mr Sargeant's death, and the need to provide answers. The thrust of the Press Statement was that there was to be no compromise on the independence of the Investigation or the transparency of the process. The Press Statement was not merely a statement to present intentions. It was an undertaking as to how things would be handled in the future,” Lord Justice Haddon-Cave and Mr Justice Swift said.

The ruling means that paragraphs 30 and 32 of the Operational Protocol relating to oral evidence being heard in private and the ability of the family’s lawyers to ask questions of witnesses will now need to be reviewed, Mrs Sargeant’s lawyers Hudgell Solicitors said.

Neil Hudgell said: “The Sargeant family were completely unaware of the actions of the First Minister behind the scenes, despite his assurances of independence. It is hugely regrettable that they have had to take matters before the High Court to shine a light on what have proven to be empty words from the former First Minister. Today’s ruling does at least address some of the long-held concerns they had about the independence of the inquiry.

“I hope that the Welsh Government and the inquiry chair will now move swiftly to meaningfully consult with the Sargeant family about a revised Operational Protocol. However, I would remind everyone that there are no victors in this process. The Sargeant family are still without a much-loved husband, father, son and brother.”